Checking for workstation lock/unlock change with c#

A SessionSwitch event may be your best bet for this. Check the SessionSwitchReason passed through the SessionSwitchEventArgs to find out what kind of switch it is and react appropriately.

You can get this notification via a WM_WTSSESSION_CHANGE message. You must notify Windows that you want to receive these messages via WTSRegisterSessionNotification and unregister with WTSUnRegisterSessionNotification.

These posts should be helpful for a C# implementation.

http://pinvoke.net/default.aspx/wtsapi32.WTSRegisterSessionNotification

http://blogs.msdn.com/shawnfa/archive/2005/05/17/418891.aspx

http://bytes.com/groups/net-c/276963-trapping-when-workstation-locked

You can use ComponentDispatcher as an alternative way to get those events.

Here's an example class to wrap that.

public class Win32Session{    private const int NOTIFY_FOR_THIS_SESSION = 0;    private const int WM_WTSSESSION_CHANGE = 0x2b1;    private const int WTS_SESSION_LOCK = 0x7;    private const int WTS_SESSION_UNLOCK = 0x8;    public event EventHandler MachineLocked;    public event EventHandler MachineUnlocked;    public Win32Session()    {        ComponentDispatcher.ThreadFilterMessage += ComponentDispatcher_ThreadFilterMessage;    }    void ComponentDispatcher_ThreadFilterMessage(ref MSG msg, ref bool handled)    {        if (msg.message == WM_WTSSESSION_CHANGE)        {            int value = msg.wParam.ToInt32();            if (value == WTS_SESSION_LOCK)            {                OnMachineLocked(EventArgs.Empty);            }            else if (value == WTS_SESSION_UNLOCK)            {                OnMachineUnlocked(EventArgs.Empty);            }        }    }    protected virtual void OnMachineLocked(EventArgs e)    {        EventHandler temp = MachineLocked;        if (temp != null)        {            temp(this, e);        }    }    protected virtual void OnMachineUnlocked(EventArgs e)    {        EventHandler temp = MachineUnlocked;        if (temp != null)        {            temp(this, e);        }    }}